White, sealable, thermoformable, biaxially oriented and coextruded polyester film containing a cyclooelfin copolymer, method for producing the same and the use thereof

Abstract

The invention relates to a white, sealable, thermodeformable, biaxially oriented and coextruded polyester film that comprises at least one base layer B and at least one sealable cover layer A, wherein at least the base layer B contains a polyester starting compound and a cycloolefin copolymer (COC). The polyester starting compound should contain an increased amount of diethylene glycol, polyethylene glycol or isophthtalic acid. The invention further relates to a method for producing the inventive polyester film and to the use thereof for thernoformed articles, especially on high-speed machines.

Patent claims:  
     
         1 . A white, sealable, biaxially oriented, thermoformable and coextruded polyester film encompassing at least one base layer B and at least one sealable outer layer A, both composed of thermoplastic polyester, wherein at least the base layer B also comprises, besides polyester, an amount in the range from 2 to 60% by weight of a cycloolefin copolymer (COC), based on the weight of the base layer B, where the glass transition temperature T g  of the cycloolefin copolymer (COC) is in the range from 70 to 270° C., and wherein the polyester contains an increased amount of diethylene glycol and/or polyethylene glycol and/or isophthalic acid.  
     
     
         2 . The white, sealable polyester film as claimed in  claim 1 , wherein the cycloolefin copolymer (COC) comprises polynorbornene, polydimethyloctahydro-naphthalene, polycyclopentene, or poly(5-methyl)-norbornene, and has a glass transition temperature T g  in the range from 90 to 250° C.  
     
     
         3 . The white, sealable polyester film as claimed in  claim 1  or  2 , wherein the COC has a glass transition temperature T g  in the range from 110 to 220° C., and wherein the polyester for the base layer B and for the outer layer A or for other outer layers contains an amount of ≦0.5% by weight, preferably ≦1.0% by weight, particularly preferably ≦1.2% by weight, of diethylene glycol, and/or contains an amount of ≦0.5% by weight, preferably ≦1.0% by weight, in particular ≦1.2% by weight, of polyethylene glycol, and/or contains an amount in the range from 3 to 10% by weight of isophthalic acid.  
     
     
         4 . The white, sealable polyester film as claimed in one or more of  claims 1  to  3 , which has a whiteness of more than 70% and an opacity of more than 55%.  
     
     
         5 . The white, sealable polyester film as claimed in one or more of  claims 1  to  4 , wherein the sealable outer layer A comprises a polyester copolymer which contains an amount in the range from 40 to 95 mol % of ethylene terephthalate units and contains an amount in the range from 60 to 5 mol % of ethylene isophthalate units, based on the total amount of carboxylic acid units, and wherein the monomer units derive from aliphatic, cycloaliphatic or aromatic diols.  
     
     
         6 . The white, sealable polyester film as claimed in one or more of  claims 1  to  5 , wherein the sealable outer layer A has a thickness in the range from 0.2 to 5.0 μm, and has a minimum sealing temperature of ≦200° C.  
     
     
         7 . The white, sealable polyester film as claimed in one or more of  claims 1  to  6 , which has a total thickness in the range from 4 to 500 μm, preferably from 8 to 300 μm, in particular from 10 to 300 μm.  
     
     
         8 . The white, sealable polyester film as claimed in one or more of  claims 1  to  7 , characterized in that the roughness of the sealable outer layer A, expressed via its R a  value, is less than or equal to 100 nm, preferably ≦80 nm, and that its value measured for surface gas flow time is in the range from 50 to 4 000 s.  
     
     
         9 . The white, sealable polyester film as claimed in one or more of  claims 1  to  8 , wherein an intermediate layer has been arranged between the COC-containing base layer B and the sealable outer layer A.  
     
     
         10 . The white, sealable polyester film as claimed in one or more of  claims 1  to  9 , which has another outer layer C whose coefficient of friction (COF) with respect to itself is smaller than 0.7, preferably ≦0.6, and whose roughness, expressed via its R a  value, is ≧30 nm, and whose value measured for surface gas flow time is in the range below 500 s.  
     
     
         11 . The white, sealable polyester film as claimed in  claim 10 , wherein the outer layer C comprises an amount of pigments in the range from 0.1 to 10% by weight, preferably from 0.12 to 8% by weight and in particular from 0.15 to 6% by weight.  
     
     
         12 . A process for producing a polyester film as claimed in  claim 1 , which comprises compressing and plasticizing, in separate extruders, the polymer or the polymer mixture for each of the layers, then simultaneously pressing the melts through a flat-film die (slot die), drawing off the extruded multilayer film on one or more take-off rollers, then biaxially stretching and heat-setting the resultant prefilm, and, where appropriate, corona- or flame-treating the prefilm on a surface intended for treatment.  
     
     
         13 . The process as claimed in  claim 13 , wherein cut material arising directly during production of the film is reused for film production in the form of regrind in an amount in the range from 10 to 70% by weight, based on the total weight of the film.  
     
     
         14 . The use of a white, sealable film as claimed in one or more of  claims 1  to  11  for producing thermoformed packaging for foods or other consumable items which are sensitive to light and/or to air, or for use in industry in the production of stamping foils, or as a label film or for the production of thermoformed moldings of any type, or for image-recording papers, printed sheets, or magnetic recording cards.  
     
     
         15 . The use of a white, sealable polyester film as claimed in one or more of  claims 1  to  11  as interior decoration, for the construction of exhibition stands or for exhibition requisites, as a display, for placards, in the lighting sector, in the fitting out of shops or of stores, as a promotional item, as a laminating medium, for protective covers of materials, or in electrical applications, in particular on high-speed machinery.